15 Million Americans Take Supplements That Could Be Toxic to the Liver, Say Researchers

Millions of Americans are supplementing their diet with potentially toxic ingredients, according to a new study published in JAMA Network Open.

After sifting through national survey data, a research team from the University of Michigan estimated that 4.7% of US adults regularly consume at least one of six botanicals potentially toxic to the liver.

Additional additives

Most herbal and dietary supplements bought in the US consist of fish oil, vitamins such as vitamin D and vitamin B12 or minerals like calcium and zinc. Herbal supplements make up between 5-12% of the market.

Despite accounting for fewer sales than other supplements, these kinds of products have become more notorious in recent years for having discrepancies between the ingredients on the label and the ingredients they contain – which, in some documented cases, include chemicals that can enhance the bioavailability of the supplement, potentially leading to liver damage.

According to Michigan researchers, this contamination issue is partly due to a lack of regulatory requirements from the US Food and Drug Administration (FDA).

To gauge the proportion of Americans who consume such herbal products, the researchers accessed data from the Drug Induced Liver Injury Network (DILIN), a multicenter US program that collects data from patients with hepatotoxic (liver-toxic) effects attributed to drugs and herbal products.

After assessing data taken from 9,685 adults (average age of 47.5), the researchers found that 731 (7.5%) reported consuming at least 1 herbal product in the past 30 days. These consumers tended to be older, female and living with a health condition such as hypertension, diabetes, arthritis or cancer.  

Turmeric was the most frequently taken supplement type, followed by green tea, ashwagandha (a shrub purported to treat anxiety), Garcinia cambogia (a fruit purported to help with weight loss), red yeast rice (a traditional Chinese medicine believed to lower cholesterol) and black cohosh (a flower purported to treat menopausal symptoms).

Most surveyed participants reported consuming such products without the advice of a doctor. 

The most common reason given for choosing to do so was to improve or maintain health. 

By extrapolating their data, the research team estimated that 15,584,599 US adults (4.7% of the population) use at least 1 of the 6 potentially hepatoxic products in the average month.

“Our interest started when we saw cases of liver toxicity from herbal and dietary supplement use in people enrolled into the ongoing National Institute of Health-funded DILIN study,” said Alisa Likhitsup, a clinical assistant professor of medicine at the University of Michigan and lead author on the paper. 

“But it was difficult to say how many people were using these supplements and why. The major finding here is the large number of Americans taking these products with an estimated 15 million adult Americans taking them on a regular basis.” 

Indeed, Likhitsup and her colleagues were surprised by the size of the figure they arrived at.

“We weren't aware that so many people were taking these supplements,” she added. “When doctors see patients in the office, they don't necessarily ask about supplement use or take into consideration their effects.”

Cause for concern

Given the known issue of mislabeling among herbal products, the researchers were concerned by their findings.

“In a previous study, we found that there was a great deal of mislabeling of some of these products,” said Robert Fontana, a hepatologist and professor of medicine at the University of Michigan.

“We performed analytical chemistry and found about a 50% mismatch between stated ingredients on the label and what they actually contained, which is quite alarming. If you buy a supplement and it says it has a certain ingredient, it's basically a coin flip if that’s true or not.”

The proportion of hepatotoxic cases across the US has nearly tripled in recent decades, from 7% between 2004-2005 to 20% between 2013-2014. 

Transplants are also on the rise. A study published in 2022 found a 70% increase in liver transplants due to injury caused by supplements from 2010-2020, compared to 1994-2009.

“We're not trying to create alarm,” Fontana said. 

“We're just trying to increase awareness that the over-the-counter supplements people are taking and buying have not been tested nor necessarily proven to be safe.” 

Reference: Alisa Likhitsup A, Chen VL, Fontana, RJ. Estimated Exposure to 6 Potentially Hepatotoxic Botanicals in US Adults. JAMA Netw Open. 2024. doi: 10.1001/jamanetworkopen.2024.25822

This article is a rework of a press release issued by the University of Michigan. Material has been edited for length and content.